Energy-dependent shielding performance of high-Z epoxy composite shielding media for radioactive waste drums: A Monte...

Lead-free polymer-based composites are increasingly investigated as alternatives to conventional heavy shielding materials; however, most studies rely on slab-based attenuation metrics that do not directly reflect dose reduction in realistic waste-package geometries. In this work, the energy-dependent shielding performance of epoxy-based composites loaded with high-Z fillers (Bi₂O₃, WO₃, and BaSO₄) is evaluated as candidate shielding media for radioactive-waste drum applications using Monte Carlo radiation transport simulations. A three-dimensional 200-L drum geometry was modeled in PHITS, and five representative gamma-emitting radionuclides spanning low to very high photon energies (Am-241, Ba-133, Cs-137, Co-60, and Na-24) were investigated. Shielding performance was assessed using spatially resolved photon flux and dose fields (2D x-z maps), centerline profiles, flux-field histograms, and a plane-integrated flux metric normalized to reinforced concrete. The results show a very high energy dependence of material ranking. For Am-241, optimized mixed-filler epoxy media reduce the plane-integrated photon field by 94% relative to concrete (≈16× lower), whereas for Ba-133 reductions of 65-67% are achieved. At intermediate energies (Cs-137; Co-60), performance differences compress, with epoxy alternatives providing consistent reductions of 27-39%. For the highest-energy case (Na-24), a WO₃-rich composite becomes dominant, yielding 78% lower integrated flux than concrete. Dose-rate analyses derived from PHITS T-Deposit tallies and inverse-square scaling confirm that these material trends translate directly into reduced external dose rates and relaxed distance-time exposure constraints. The current study demonstrates that optimized epoxy-based shielding media can substantially improve drum-scale shielding performance, with the optimal composition highly dependent on the photon energy spectrum of the waste.